The invention concerns a device for applying a cable onto a rotating receiving surface, in particular for the manufacture of tires.
The benefit of incorporating annular reinforcement in tires, that can be used all around their circumference, such as a carcass reinforcement, was demonstrated a long time ago. Such reinforcement can in particular consist of a ply comprising cables wrapped radially on the tire carcass; this ply is currently referred to in the vulcanized tire as the xe2x80x9czero-degree ply.xe2x80x9d
Here, the term xe2x80x98cablexe2x80x99 means one or more textile or metallic cords; said cord or cords, moreover, can be coated with a raw or cured rubber mixture.
Metallic cords in particular are used to make the zero-degree ply in certain tires such as those designed for heavy loads. Now, during the vulcanization of the uncured tires, the tires undergo a shaping process in the vulcanization mould which must be taken into account for the final structure of the tires. It is clear that the use of metallic cables for zero-degree plies involves great difficulties, since the rigidity of these cables does not allow them to elongate during shaping in the mould.
Various solutions have been considered for overcoming this problem. One solution was to use subdivided metallic cables. Zero-degree plies made in that way can conform to the elongation to which the tire is subjected during vulcanization. Such plies, however, constitute zones in the vulcanized tire which are more susceptible to oxidation because of the cuts between the different sections of the cable. This solution is therefore unsatisfactory.
Other solutions have been proposed, which relate to the nature of the metallic cables. For example, the use of bi-elastic metal cords makes it possible to achieve a compromise between the rigidity and elongation properties of the uncured ply obtained. Although interesting, such a solution entails considerable modifications in the desired uncured and vulcanized structures of the tires, to compensate for the lower rigidity of the vulcanized zero-degree ply obtained, such as the presence of an additional ply, modifications of the rubber mixtures, etc.
Finally, a third approach was to modify the positioning of unvulcanized products so as to obtain desired structures after vulcanization. This led to the idea of positioning the cables in an undulating shape in the unvulcanized tire, so that they will be arranged radially in the vulcanized tire by virtue of the shaping that takes place in the vulcanization mould.
This intelligent solution, however, still presents difficulties in being put into practice.
In effect, the unvulcanized tire has been built up on a cylindrical or slightly curved drum, while the vulcanized tire emerging from the vulcanizing mould is more markedly curved compared with its initial shape. Consequently, during shaping, the deformations undergone by the tire will be much larger at the crown of said tire than at its shoulders. It is therefore necessary to be able, in an industrial operation, to position a cable sinusoidally with different undulations, or even different periods, according to its radial position so that the ply produced will have cords orientated radially whatever its radial position near the crown or the shoulders.
European Patent Publication EP-0 724 949 describes a device for applying textile or metallic cords on a rotating surface with sinusoidal undulations. Such positioning may be achieved by means designed to displace the cords in transverse translation relative to their feed direction, the amplitude and period of the sinusoid being regulated by measuring and regulating the rotation speeds of the positioning surface, the element feeding the cords, and the control of the displacement means. However, said displacement means consist of a cord feeder that can be moved in the transverse direction, actuated by a motor via a connecting rod attached to a motorized wheel.
In practice, this means that since the rotation speed of the positioning surface is fixed, to modify the undulation amplitude of the cords on that surface continuously the speed of the element feeding the cords must be varied in order to modify the quantity of cord fed in and the position of the connecting rod relative to the wheel must be varied in order to synchronize the amplitude modification of the undulations produced. It seems difficult to achieve this last modification continuously. Moreover, it is clear that as a function of the sinusoid desired, the positioning speed too must be limited so as not to disturb the motorized movement of the cord feeder.
The aim of the invention is to overcome this combination of difficulties.
According to the invention, the device for applying at least one cable onto a rotating receiving surface having a linear surface speed V2 comprises a body with means for feeding the cable that comprise at least one rotatable capstan producing a cable linear speed V1, means to displace the cable transversely relative to the receiving surface and means to position the cable on said receiving surface, characterized in that the amplitude of the transverse displacement of the means to displace the cable transversely is controlled directly as a function of the ratio between the speeds V1 and V2, and said amplitude can be modified continuously during the positioning of the cable.
Thus, said control enables continuous modification of the amplitude of the sinusoid formed, but above all it enables very high cable positioning speeds to be achieved.
The objective of the invention is accordingly a device for applying at least one cable onto a rotating receiving surface having a linear surface speed V2, with means to feed the cable that comprise at least one capstan revolving to produce a cable linear speed V1, means to displace the cable transversely relative to the receiving surface, and means to position the cable on said receiving surface, characterized in that the means to displace the cable transversely effect said displacement by the combination of a rotary movement about an axis perpendicular to the cable travel direction with a pivoting movement in a plane containing the axis of said rotation, the extent of pivoting being determined by the ratio between the speeds V1 and V2.
The invention also relates to a process for applying at least one cable onto a rotating receiving surface, in particular during the manufacture of tires, which comprises the following stages:
a cable is fed in a direction essentially perpendicular to the rotation axis of the receiving surface;
the cable is displaced transversely to said surface to produce undulations on the latter; and,
the cable is positioned on said receiving surface,
characterized in that the transverse displacement of the cable is obtained by the combination of a rotary movement about an axis perpendicular to the cable travel direction with a pivoting movement in a plane containing the axis of said rotation, the extent of pivoting being determined by the quantity of cable fed per revolution of the receiving surface.